Question

String [] tableTypes = { "TABLE" };
    DatabaseMetaData md = (DatabaseMetaData) dbConnection.getMetaData();
    ResultSet rs = md.getTables(null, null, "%", tableTypes);
    while (rs.next()) {
        System.out.println(rs.getString(3));
    }

我使用这部分代码从我的本地oracle数据库获取所有表，但我需要更改它以便只返回只有一个主键的平板电脑。有任何想法吗？

Answer 1

你可以对该循环中的每个表使用DatabaseMetaData.getPrimaryKeys()：

String [] tableTypes = { "TABLE" };
DatabaseMetaData md = dbConnection.getMetaData(); // the cast is unnecessary!
ResultSet rs = md.getTables(null, null, "%", tableTypes);
while (rs.next()) 
{
  String schema = rs.getString(2);
  String table = rs.getString(3);
  ResultSet pkRs = md.getPrimaryKeys(null, schema, table);
  int colCount = 0;
  while (pkRs.next()) 
  {
     colCount ++;
  }
  pkRs.close();
  if (colCount = 1) 
  {
      System.out.println("Table " + table + " has a single column primary key");
  }
}

然而，这将是非常慢。使用直接从user_constraints和user_cons_columns检索此信息的查询将更快批次：

select col.table_name, count(*)
from user_constraints uc
  join user_cons_columns col 
    on col.table_name = uc.table_name 
   and col.constraint_name = uc.constraint_name
where constraint_type = 'P'
group by col.table_name 
having count(*) = 1;

Answer 2

您可以使用此代码：

static Statement statement = null;
static ResultSet result = null;

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    // TODO code application logic here
    try {

        Class.forName(driverClassName);
        dbConnection = DriverManager.getConnection(url, username, passwd);

        statement = dbConnection.createStatement();

        String[] tableTypes = {"TABLE"};
        DatabaseMetaData dbmd;
        dbmd = dbConnection.getMetaData();

        result = dbmd.getTables("%", username, "%", new String[]{tableTypes[0]});
        while (result.next()) {
            String tableName = result.getString("TABLE_NAME");
            ResultSet tempSet = dbmd.getPrimaryKeys(null, username, tableName);

            String keyName="";
            int counter=0;
            while (tempSet.next()) {
                keyName = tempSet.getString("COLUMN_NAME");
                counter++;

            }
            if(counter == 1) {
                System.out.println(tableName);
            }
        }
    } catch (Exception e) {
    }
}

Answer 3

表最多可以有一个主键。该初级可以是复合的 - 即由多个柱组成。另一个（第二个）键可能是UNIQUE（+ not NULL），它与primary不完全相同。

如何检查列的最佳方法是查询ALL_CONTRAINTS视图。 JDBC方法DatabaseMetaData只有有限的功能。

使用DatabaseMetaData Java在oracle中查找没有复合主键的表

3 个答案: